1. Field of the Invention
The present invention relates to a motor, in particular, a motor having two-layer circuit boards.
The motor is used for office automation related equipment such as laser beam printers (hereinafter abbreviated as “LBP”) and copying machines as well as computer-related equipment.
2. Description of the Related Art
A DC motor generally used for LBPs and copying machines will be described with reference to FIG. 8. To be easily understandable, an upper side in the figure, that is, a rotor side in the motor shaft direction is assumed as an upper side and a lower side in the figure as a lower side in the following description.
Configuration—FIG. 8 is a cross-sectional view showing configuration of a motor 11 conventionally used in LBPs, copying machine, etc. The motor 11 has a static member 22 by which the motor fixed to a product such as a LBP or a copying machine, a bearing 7 located between the static member 22 and a rotational member 3 to support the rotational member rotatably with respect to the static member 22 through the bearing 7.
The static member 22 and the rotational member 3 will be described in detail below.
Static member 22—The static member 22 has a bracket 5 for fixing the motor 11 to the product, a cylindrical sleeve 30, the lower part of which is penetrated into a through hole formed at the bracket 5 and fixed thereto, a circuit board 9 fixed to the lower side of the sleeve 30 and a stator 10 fixed to the peripheral surface on the upper side of the sleeve 30.
The bracket 5 is a plate-like member at which the through hole is formed. A fitting piece 12 with a screw inserting hole is formed one stage lower at four corners of the bracket 5 with being folded, thereby fixing the motor 11 to the product. A connecting piece 13 is formed one stage higher at an end part of the bracket 5 with being folded, so that the circuit board 9 is held fixedly and grounded electrically.
The sleeve 30 is a substantially cylindrical member having a through hole at the center thereof and a flange supporting part 25 on the periphery of the lower side thereof. A supporting plane of the supporting part 25 at the upper side supports the circuit board 9 and a supporting plane of the supporting part 25 at the lower side is supported by the bracket 5.
The circuit board 9 is connected with keeping an electric continuity to the bracket 5 through the connecting piece 13. The circuit board 9 has a circuit components mounting part 26 for mounting a circuit thereon in the region where is not a region opposed to a rotor 19. A circuit component for rotationally driving the rotor 19, that is, a control circuit component 14 for controlling conduction to a stator coil is mounted on one plane of the circuit components mounting part 26.
Rotational member 3—The rotational member 3 has a shaft 20 rotatably supported to the static member 22 through the bearing 7 and the cup-like rotor 19 is fixed to one end of the shaft 20.
The shaft 20 has a cylindrical shape extending in axial direction, which is rotatably supported via the bearing 7 in an inner side of the through hole of the sleeve 30. A rotor 19 is fixed to the upper end of the shaft 20 so as to penetrated thereinto.
The rotor 19 is a cup-like member that has a disc-like bottom part extending in radial direction from the shaft 20 and a cylindrical side parts extending from the bottom part in axial direction. A cylindrical magnet 18 is fixedly fitted onto an inner periphery of the side parts and opposed to the stator 10 fitted onto the sleeve 6 with a small space therebetween.
Operation—When driving current by which magnetic fields are excited around the stator 10, is applied to a three-phase coil of the stator 10, suction and repulsion forces are generated by a mutual interaction between the stator 10 and the magnet 18, thereby to generate a rotational force in the rotor 19. This rotational force is transmitted to the inside of the product through the shaft 20 fixed to the rotor 19.
Circuit board—The circuit board 9 has the circuit components mounting part 26 for mounting a circuit thereon in the region where is a region not opposed to the rotor 19. In other words, when the motor is viewed from an upper side in axial direction, the circuit component mounting part 26 has a larger area in comparison with the area of the motor 11. For this reason, in the case that product such as a LBP or a copying machine is provided with the motor 11, it is necessary to ensure an enough space corresponding to the circuit component mounting part 26 on the circuit board 9.
However, in some products, it may be difficult to ensure such sufficient space on the circuit board 9. In such case, a reduction in space corresponding to the circuit component mounting part 26 is desired.
To address the desire, one possible solution is to adopt two-layer configuration in which the circuit performing an entire control for the motor is separated into two parts and these are allocating into two boards then the two boards are arranged in two layers located in axial direction with a distance. In a general two-layer configuration, a distance between two circuit boards in the axial direction is kept by using cylindrical spacers disposed in the vicinity of the periphery of the circuit boards. Screw holes are formed on the two circuit boards at positions where the board spacers are arranged. Accordingly, the two circuit boards are fixed to fixing members of the motor by screws with sandwiching the board spacers there-between.
This two-layer circuit board configuration requires the spacer to ensure a distance between a first circuit board and a second circuit board. This causes a problem of increasing the number of components and the corresponding costs.